In the process of manufacturing semiconductor devices or flat panel display devices (FPD), liquid processes are frequently used, in which a process liquid is supplied onto a target substrate, such as a semiconductor wafer or glass substrate. For example, processes of this kind encompass a cleaning process for removing particles and/or contaminants deposited on a substrate.
As a substrate processing apparatus used for this purpose, there is known an apparatus in which a substrate, such as a semiconductor wafer, is held on a spin chuck, and a process liquid, such as a chemical liquid, is supplied onto the wafer, while the wafer is rotated, so that a cleaning process is performed. In general, an apparatus of this kind is operated such that a process liquid is supplied onto the center of a wafer or substrate, and the substrate is rotated to spread the process liquid outward, so as to form a liquid film and throw off the process liquid outward from the substrate. Then, after the cleaning process, a rinsing liquid, such as purified water, is supplied onto the substrate while the substrate is rotated in the same way, thereby performing a rinsing process to form a liquid film of the rinsing liquid and throw off the rinsing liquid outward from the substrate. In light of the processes described above, a drain cup is disposed to surround the substrate to receive and discharge the process liquid or rinsing liquid thrown off outward from substrate (for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-368066).
In substrate processing apparatuses of this kind, when a rinsing process is performed on a substrate after a cleaning process is performed by use of a process liquid, such as an alkaline chemical liquid or acidic chemical liquid, it is necessary to remove not only the process liquid on the substrate but also the process liquid left on the drain cup. Specifically, if the alkaline chemical liquid or acidic chemical liquid are left on the drain cup after the rinsing process, the substrate drying performance is adversely affected by formation of salts due to evaporation of the chemical liquid or reaction between alkaline and acidic chemical liquids continuously used for the cleaning process. Where a plurality of chemical liquids, such as an alkaline chemical liquid and an acidic chemical liquid, are collected and reused, the chemical liquids are mixed with each other and thereby degraded at higher rate. Accordingly, the process liquid left on the drain cup should be sufficiently removed by a process performed along with or separately from the rinsing process periodically or as needed.
However, in conventional rinsing processes, the rinsing liquid cannot be sufficiently supplied overall inside the drain cup, and so the process liquid is left inside the drain cup, and makes it difficult to solve the problem described above. There is a case where the drain cup is provided with a cleaning mechanism for performing a cup cleaning process, but this brings about problems such that the apparatus becomes complex and bulky.